One of those major side effects is ipsilateral phrenic nerve paresis. This is because blockade of the brachial plexus at the interscalene groove with a single large-volume injection causes diaphragmatic hemiparesis in 100% of patients. This incidence is decreased to 20% with a continuous infusion of a dilute solution11, where 9% of patients have a subjective feeling of shortness of breath. An ideal infusate in CPNBH would control postoperative pain and have minimal effects on the phrenic nerve.